Thermal relay



Sept. 16,

A. P. JACKEL THERMAL RELAY Filed Dec. 30, 1949 [baa/b66012.

inflame i012.

INVENTOR.

Art/f? JZJc e Patented Sept. 16, 1952 UNITED; STATES PATENT ore-l es Arthur: P; Jackel; Penn Township, Allegheny County-7; Pai assignor to Westinghouse Ai'r BrakeiCompany alcorporationof Pennsylvania My invention relates to: relays;1; and: particu' larly to relays which employ:'a.-therma1ly responsive element heated by-an-energy'transfermeans for operating electrical contacts: at the expiration of a predeterminedtime interval afterthe application of operatingenergy to-the relay;

In relays of this type, the operating energy is supplied to the heater" element-front a source which is? sometimes subj ect to voltagevariations. Forexample; the relayzmight be energized from a storage battery whiclrat tiines wouldbe fullycharged, and-at other times'would' be in a'=par-'-' tially discharged "condition'thus causing the volt-- age applied to' therelay tobelimerat sometimes than others. This variation in the applied voltage ofthe operating energycauses the heater element-to; heat more slowly: at 1 some times than others. and thetime required for the heated thermally responsive element: to operate-the relay contacts l therefore'varies inversely with the appliedrvoltage. This iseObV-iOllSlY undesirable; and one: object of: my: invention isto providemore nearly uniform performance of such relays at various voltages-1 Another object of: my: inventionis to' provide novel means .for: operating the electrical contacts inaithermal relay with:a snap'action;

stiltanotherrobject of myinventionis -to maintain: the; relay: operation substantiallyindependents'ofi theambient temperature to which thelrelay'is. exposedi In. the: preferred form "of? myiinventi'on Ii'accomplisht. thesei .objects= by providing: the relay with. electrical contacts secured 'tot two thermally responsive: members; An::energy transfer means such asta'xheating elementheats thev first ther mally responsive member rand thereby causes it to:defle'ct.. Also: an electromagnetict'means is pro=- vided for: applying-to the 'firstimember' a: force which opposes-the'deflection causedbythe' energy transfercmeans:v This: force; is: proportioned to compensate for-variationsiin the operatingtime of'tthe relay caused? by variations in: the app'lied voltage.v That is" toi say; the energy: transfer means i and the electromagnetic means are energized by the sam'e 'source so that'whentherelay is energized, the magneti'c force due'to the 'energization of the electromagnetic means acts on'the'first thermallyresponsive memberat the same time the energy transfer means begins heatingthe member causing it to deflect; The magnetic force prevents the deflection-"of the member'from actuating the electrical contacts until the deflection force becomes greatenough to overcome the-magnetic force: Wl ienthis occurs; the com- 2-1 tactstopen with asnapi-actiona However, the electromagnetic means; is supported by the second thermally responsive:member in such man ner that ambient temperature variations causes. 1 the deflection/of.both-.ofthe-thermally responsive members to maintain theelectrical contacts. ina substantially constant. relationship. The time interval for operating the contacts of thezrelayis: thereby, made essentially independent: ofvoltage: variations and ambient. temperature.

Other'objectspand characteristic'features of my invention will become; apparent aszthe description proceeds;

I' shall describe one formaoirelay embodying my invention, and shall thenpointrouttheznovel features thereof in claims.

In thexaccompanyingdrawings Fig 1.is. a view, partly inside elevation andpartlydiagr-ammatic, showing one form of. thermal relay embodying my invention. Fig; 2 is a bottom viewof the relay 'shownin; Fig. 1. Fig. 3-is.aview of. the left side of therelay as seen-in Fig. 2;

Likereference charactersrefer to similar, par-ts inieach of'the views.

Referring; to the drawings, the. thermal relay here shown: consists of a. pluralitys'oi insulating blocks I held together-by; two. insulated screws 2Jscrewed intoamounting-m'ember. 2a; clamped between the blocks l in parallel spaced relations are four'terminal fingers 3a, 3b,'..3c.and.3d; Also clamped between thee blocks l are atfirstsupport 4' disposed adjacenttfinger. 3a; and;.a':.sec, ondsupport 5'disposed below-thersupport 4' and adjacent finger 30. A first thermally'responsive member, here shown as a bimetallic strip 6,1 is secured atone end tothesupport: 4: Secured to the strip B at its free'end is anelectrical'ccntact element 1 which cooper-ateswithan electrical contact element 8,- securedito. oneend ofrla second bimetallic strip 9, totformzaacontact .l-B; The strip 9 is' disposed below: and'substantially parallel to strip 6 and is securedzat'itsi other. end to the support5. Thecontact formediby' the contact elements- 1 and 8 is" adapted to. bexopened and closed in order. to'openiandclose an electritcal' circuit including: this contact,. the supports 4 and. 5, and the terminal: fingers-.312 and 30. To compensatefor the'effects on the contact '1-8 of variations" in ambient temperature; thelbi-r metallic strips 6 andQ are:di'sposed;so that the unsecured end of each stripzdefleets; downwardly as a'result'of increases in. ambientrtemperature.

Secured to the support 5;lin .addition to'the bimetallicstrip 9, istan' L-shaped member 1| Oldie posed withx'oneleg' 1 0a substantially parallel; to

g, 3 the bimetallic strip 9. Mounted on the leg Ilia is a heating element 13 which is electrically connected to the terminal fingers 3b and 3d and whichis adapted to heat the strip 9 by conduction along the member Hi when the heating element is energized. The heating element I3 is arranged to be energized from a suitable source, here shown as a battery B, over a circuit which includes a switch S.

It will be apparent from the drawings that when the switch S is closed the heating element i3 is energized and begins to heat the strip 9. After a predetermined time the strip 9 is willciently heated to deflect downwardly and open the contact 7-3.

Relays of the type thus far described are well known in the art. In relays of this type, when the voltage decreases at the source B the element it heats more slowly than normally, and when the voltage increases at the source 13 the element i3 heats faster than normally. As a result, the time required for the heated bimetallic strip 9 to actuate the contact l--3 varies with the voltage. Moreover relays of the type thus far described are subject to contact difiiculties due to the arcing which occurs when the contact 'l--8 opens gradually in response to the heating of the strip 9.

According'to my invention, I overcome these difficulties by providing the relay with an electromagnetic means disposed to oppose the operation of the electrical contacts in response to heating of the heating element It. As here shown, this means comprises an electromagnet I l attached to the unsecured end of the bimetallic strip 6, and provided with salient poles which cooperate with an armature !5 attached to the unsecured end of the bimetallic strip 9. The electromagnet. It is intended to be energized by the same source B as the heating element l3', and the switch S controls the energy supplied to-the electromagnet it 'as shown in Fig. l. 'When'the switch S is closed,

the source B in addition to energizing the heating element l3, energizes the ele'ctrornagnet i l. The electromagnet it exerts a magnetic force pulling armature l5 and the unsecured end of strip 9 toward the unsecured end of strip 6, and resisting the deflection force pulling the contact elements 'i-B apart. The magnetic force prevents the defiection of strip 9 from pulling the contact elements 7 and 3 apart until the strip 9 is sufiicientlyheated to overcome the magnetic force. When this occurs the contact l8 opens with a sudden snap action. V Q

It will be readily understood that since the electromagnet id and the heater element :3 are energized by the same source, the voltage variations at the source will result in voltage variations at the electromagnet It proportional to the voltage variations at the heater element Hi; When the applied voltage is lower than normal the magnetic force or the electromagnet It on the armature i5 is less than normal. The required deflection force of the bimetallic strip 9 necessary to overcome the magneticiorce is also less than normal. But thestrip 9 is heated more slowly when the voltage at the heater element [3 is lower than normal. Therefore the time required for the strip 9 to actuate the contact l -8 is substantially the same as at normal voltage. Similarly, when the applied voltage is higher than normal the magnetic force of the electromagnet [4 on the armature I5 is greater than normal. The required defiection force of the bimetallic strip 9 necessary to overcomethe magnetic .force is also greater than 4i normal. But the strip 9 is heated faster when the voltage at the heater element I3 is higher than normal. It follows therefore, that by properly proportioning the parts, the time required for the strip 2 to actuate the contact l'-8 can be made to be substantially independent of voltage variations.

One advantage of a relay constructed in accord ance with my invention is that since the thermally responsive members are arranged to deflect in the same directions in response to ambient temperature changes in the manner previously described, and since the 'electromagnet of the electromagnetic means for compensating for variations in voltage is secured to one of these members and its cooperating armature to the other of these members, it follow that changes in ambient temperature will not change the relative position of the electromagnet and its cooperating armature, and therefore will not afiect the voltage compensation provided by my invention.

It should be particularly pointedout that while in'describingmy invention I have shown it applied to a thermal relay of the type employing bimetallic strips as the thermally responsive members, it may be applied to many other types.

of thermal relays,

Although I have herein shown and described only one form of thermal relay embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what i claimis: r

1. In a thermal relay, in combination, two cooperating thermallyr-esponsive members provided with electrical contacts, one of said thermally responsive members being provided with an energy transfer means that causes said'one member to be deflected and thereby operate said contacts in a given predetermined time interval in response to energization of said energy transfer: means, said one member also being provided with an armature and the other thermally responsive member being, provided with an electromagnet having salient poles which cooperate with said armature so as to oppose the operation of said electrical contacts in response to energization of said electromagnet, the parts of said thermal relay being so proportioned that when said electromagnet and said energy transfermeans are energized from the same source of current the forces set up by saidelectromagnet and said energy transfer means willcause said contacts to become operated in said given predetermined time intervalirrespective ofvoltage variations of said current source, and said thermally responsive members being so disposed and having their parts so proportionedthat the deflection of said members due to variations in ambient temperature will'cause said electrical contacts as well as said eleotromagnet and cooperating armature to' remain in a substantially constant relationship.

In a thermal in combination, two essentially identical bimetallic members provided with electrical contacts that are normally closed, onecf said members being provided with a heating means that causes said one member to be deflected and thereby operate said contacts in a given predetermined time interval in response ,to energization of said heatingmeans, said one member also being provided with an. armature, the other member being provided with an electromagnethaving salient poles which cooperatewith said armature so as to oppose the operation of said electrical contacts in response to energization of the electromagnet, the parts of said thermal relay being so proportioned that when said electromagnet and said heating means are energized from the same source of current the forces set up by the electromagnet and heating means will cause said relay to open its contacts in said given predetermined time interval irrespective of voltage variations of said current source, and said bimetallic members being disposed in substantially parallel spaced relation and having their parts so proportioned that the deflection of said members clue to variations in ambient temperature will cause said electrical contacts as well as said electromagnet and cooperating armature to remain in a substantially constant relationship.

3. In a thermal relay of the type comprising two bimetallic strips disposed in substantially parallel spaced relation and having their parts proportioned so that the deflection of one of said strips due to variations in ambient temperature will be in the same direction and essentially of the same magnitude as the deflection of the other of said strips, said strips being provided with electrical contacts that are normally closed, said one strip also being provided with electrical heatingmeans for deflecting said one strip to open said contacts in a given predetermined time interval in response to heating of said strip, said one strip also being provided with an armature, said other bimetallic strip being provided with electromagnetic means having salient poles which cooperate with said. armature so as to oppose the opening of said contacts in response to energization of said electromagnetic means, the parts of said thermal relay being so proportioned that when said electromagnetic means and said heating means are energized from the same source of current, the forces set up by the electromagnetic and heating means will cause said relay to open its contacts with a snap action in said given predetermined time interval irrespective of voltage variations of said current source.

ARTHUR P. JACKEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,651,408 Feacocl: Dec. 6, 1927 2,022,440 Slough Nov. 26, 1935 2,181,606 Parks Nov. 28, 1939 2,311,801 Winans Feb. 28, 1943 FOREIGN PATENTS Number Country Date 17,947 Great Britain Aug. 6 1913 

